Adenosine binds to adenosine receptors at the cell surfaces to cause various biological response.
The four subtypes of adenosine receptors, including A.sub.1, A.sub.2a, A.sub.2b and A.sub.3 are known to be present (Pharmacological Reviews, Vol. 46, No. 2, p143, 1994). It is indicated that adenosine A.sub.3 receptors are highly represented in the human pulmonary tissue (Proc. Natl. Acad. Sci. USA, Vol. 90, p10365, 1993), and are related to acceleration of the release of various mediators from mast cells (J. Biol. Chem., Vol. 268, No. 23, p16887, 1993). It is also disclosed in WO 95/11681 that compounds antagonistic to A.sub.3 receptors inhibit mast cell degranulation by adenosine and are 2288733A that compounds antagonistic to A.sub.3 receptors inhibit the activation of eosinophil by adenosine and are expected as antiasthmatics. Namely, compounds antagonistic to adenosine A.sub.3 receptors are expected as antiasthmatics. Allergic diseases such as pruritus are known to be caused by the release of mediators from mast cells due to various types of stimulation [Standard Dermatology, Vol. 4. p160 (Igakushoin), 1994]. Therefore, compounds antagonistic to A.sub.3 receptors are also expected to inhibit the release of mediators from mast cells and exhibit an antiallergic action such as an antipruritic action or the like.
A paper ( J. Med. Chem., Vol. 23, p1188, 1980) discloses that as condensed purine compounds, compounds represented by formula (A) have a weak bronchodilator action. Also Japanese Unexamined Patent Publication No. 91-204880 discloses that compounds represented by formula (B) exhibit a diuretic action and a weak antiasthmatic action. ##STR2##